A long day spent making CommandCleanup actions run in a separate job pool than CommandPerform actions. I don't think this will speed anything up much yet, but it's useful groundwork. Now expensive things that are not the main action of a command can be moved into CommandCleanup and won't delay git-annex moving on to the next file. The main thing I want to move is checksum verification after a transfer. But there are probably other things I have not thought of.

CommandCleanup was always not well distinguised from CommandPerform, and so there was little incentive to put things in it. Now that's changed.

I also noticed that with -J, git-annex takes significantly longer than without to get started, when the first file it needs to process is quite a way down the ls-tree. This must be concurrency overhead. But, when CommandStart is skipping over a file that it doesn't need to process, there is no need to do that bookkeeping. Planning to take some time tomorrow to see if I can refactor CommandStart to avoid that overhead.